Mike Castoro | TapeOp

Mike Castoro, the 43-year-old owner and creator of Wunder Audio, lives quietly with his wife and two kids in the northern hills of Austin, Texas. Originally from upstate New York, he spent his junior high and high school years in Florida, then moved to Austin during the '80s to attend the University of Texas, where he earned a BA in recording engineering. Shortly after graduation, he started Stardog Studio as a modest, 4-track cassette facility, and within a decade grew it to a 24-track analog museum for vintage gear rife with Pultecs, Fairchilds, Neve, Neumanns and at least a half dozen Mellotrons — the tape-based keyboard popularized by The Beatles and the Moody Blues. After six years of running a successful studio, he branched out and became a vintage gear broker when he started a company called Misty Hill Audio. In the late 1990s, he started manufacturing his own line of pro audio equipment under the Wunder Audio banner.

How is the CM7-GT mic different from and similar to the CM7 microphone?

Well, they're similar especially if you order the GT with the M7 capsule instead of the K47 capsule. The capsule, the grille and the transformer are all going to be identical. The main difference is the GT has no pattern switch on the chrome top grille like a U47would have — it's on the power supply unit instead. So the cardioid is a perfect cardioid on the U47 or CM7, but when you change patterns using a power supply there's always variation plus or minus by a tiny percent. Still, the C12 and the M49 also change polar patterns from the power supply, and those are certainly well-accepted mics. Also, the metal work on the GT isn't historically correct like it is in the CM7, where it's as close as possible to an authentic U47. It comes from the same high quality metal shop, but it's made of different parts and a lot simpler. We don't have to replicate every tiny screw, piece of rubber and PVC in the U47.

So are you approaching the GT as a new mic entirely?

Exactly. We're doing a new mic from scratch, so we don't have to reverse engineer everything. On the GT, there's probably two thirds the parts of the CM7. For example, on the CM7, if you take off the grille, the capsule travels with it — it's connected. But if you take the grille off the GT, the capsule stays on the body of the mic. Just that one part of the equation means the GT has a lot fewer parts and lower costs. Another example is that the connector on the bottom of the CM7 is a U47-type Tuchel. On the GT we didn't want to compromise too much and use an XLR, we used a ¾ size Tuchel like you see on a U67 or an M269.

Any other differences between the two mics?

Obviously, the heart of the GT is the glass tube, which is what GT stands for. We're using a NOS Telefunken glass tube that basically replaced the VF and EF14 back in 1960 when they went to glass tubes and stopped making the metal tube. Since it has the glass housing, theoretically the microphonics should be a bit better than the metal, and I'm able to find a lot more really good quality tubes because I have thousands to choose from. Tubes make the biggest difference sonically between the two mics. The EF14 has finer detail (I think) than the glass tube and 3 dB more output. So when you do a shootout between the two mics, they're going to sound pretty identical if you set the mic pre to 3 dB more gain on the GT. The extra noise floor is equalized by the lower noise from the glass tube — the metal tubes tend to be noisier, even though they provide better detail. The other thing I noticed is that when I tried some loud, shouting type vocals the CM7 had a fuller sound than the GT, but since I did one take, I don't have a well-rounded opinion of that yet. Time will tell. It's basically the same circuit, although not point-to-point like the CM7. One engineer thought that the difference between the CM7 and the GT was that vocals sounded closer, more intimate on the CM7.

How did you go from musician/studio owner to pro audio manufacturer?

I started Stardog Studio as a singer-songwriter looking to record his own stuff. All I really had was a four-track cassette recorder and a Realistic microphone. I couldn't afford better stuff, but I was well aware there was better stuff out there. I always used to say that we would reinvest ten percent of the studio profit into new gear, but after six years I realized that wasn't happening. So I got a Small Business Administration SBA loan — this was during the Clinton Administration — and it was probably the best thing I ever did. It's a government guaranteed loan. It's hard to get a straight bank loan without collateral, but with the SBA loan they looked at my last three years of tax forms and they asked me what my five year projection was going to be, so I projected very big. They gave me a good-sized credit line and I went wild — I spent it all in about a month. Because I loved microphones, I bought way too many.

What kind of mics did you buy for Misty Hill Audio?

Neumann U47s of course, along with CMV563s, RFT 7151 bottle mics, Schoeps, and AKGs. I actually blew more money than I got from my SBA loan. It was about $100,000 and I spent $116,000. I even dipped into my credit card. I wasn't very frugal, so I sold some of the stuff and realized I could make a little profit by buying and selling vintage gear. So I started a business called Misty Hill Audio where I did that consistently for about six years. Eventually, I actually earned a huge rack of vintage gear — Pultecs, Fairchilds, Studer tape machines and Neve boards. I guess I was pretty good at what I did, because I made a lot of contacts across the country and overseas to find gear. The catch is you have to know how to tech your own gear, which I was able to do. I would buy U47s in any condition — I didn't care if they worked or not, because I knew you'd never find one that was perfect. I always said they came in varying degrees of decay. As long as all the parts were there, if it wasn't working, fine. I did lose money on deals a few times, especially when I started trading on eBay. eBay killed many vintage broker careers, but fortunately I did most of this from 1997 to 2003, before eBay got so big — although I was competing with eBay at the end.

How did you get into making your own mics?

I bought my first U47 in 1997, and it was in such bad condition that I wanted to make a new body for that mic. The grille was dented in and it looked like an old rusted pipe. Surprisingly, it sounded pretty good, and when I took it apart I had visions of being able to mill the aluminum and reconstruct the mic again fromscratch. In my mind, it didn't seem like so tough anordeal — but it sure was. I figured if the U47 was made 50 years ago, then there would be no reason it couldn't be done now. One of my uphill battles was trying to get the right metal kit for the mic so I could sell it for $5,000. Most of the metal workers weretelling me each metal kit would cost $5,000 itself. It took a long time to find a kit at a price point where it would be feasible to build a mic and sell it for $5,000. I talked to other manufacturers who wanted to do what I was doing, and they told me the target price would have to be $12 to $15,000 dollars.

So initially you were interested in repairing the U47s you already had, but then you took it a step further and decided to build your own?

Right, except initially I only wanted to make ten of them. I wanted to make a body to repair that first mic I owned, and then build nine more from scratch. In the first year, from 2003 to 2004, I only sold eight CM7s total. Even after the third year, I was selling less than 30 per year. It takes a long time to make up your investment, but I didn't care — I just wanted the mic so I could use it. And I always wanted parts for U47s. I'd think, "I wish I had a tube socket", or "I wish I had a bottom bell with a cable connector" or "I wish I had the U47 grille." And people were also buying parts from me, and still do so today. The parts I use for the CM7 you can also use to replace parts in the U47 — they fit perfectly on the original mic and there aren't too many reproductions you can say that about.

You also make a CM12, which is patterned after the AKG C12, but we don't hear much about that one. Why?

The reason you don't hear about it is for the same reason the CM7 was flying under the radar for a few years. I don't send that many mics out for review, and when a mic is in what I call the pioneering period — when there are not many sales happening — it's hard to keep extra mics to send out for review. The CM12s are about two years behind the CM7, and I only build up five at a time. That said, a lot of people have them, and some people even own pairs of them. They're pretty much a dead ringer for the C12. If you had the mic opened up next to an original C12, you'd never be able to tell the difference except for the color of the capacitors.

You also manufacture the PEQ1, PEQ1R, PAFOUR and the new Wunderbar. Are these different versions of the same preamp design?

The PEQ1, 1R and PAFOUR are all the same preamp design. Of course the PAFOUR doesn't have EQ like the others. They're like a very vague replica of the old Allotrope modules. When I say vague, there's about eight years of work starting from the reproduction to where we are now. We did change resister and capacitor values, and improved the slew rate from 5 volts per microsecond to 22 volts per microsecond, so it's a 44 times faster slew rate.

What's the slew rate?

It's just the rise time of the signal, and when it's a lot quicker it sounds more natural and realistic on the high end. That's the difference between the PEQ1 and PEQ1 with the Revision A mod. With the PAFOUR we improved the output stage a little bit. We added a five watt power amp right before it goes to the output transformer. What that does is it drives a low impedance load better, such as a vintage compressor that has transformer inputs. A lot of modern equipment will have a 10 K input impedance, while old vintage stuff might have a 600- ohm impedance. The PEQ1 is now into a revision C. We added a discrete active HP filter, a much higher quality gain switch, a custom design that has three times the gold contact area on each switch position, and we're replacing the push button switches with the light pipe switches that are found on the Wunderbar console. Even the enclosures will have improved metal work, with thicker faceplates and tack welding so everything's beefier. The PC boards have been expanded from two- sided to four-sided. We're going to have a radio frequency filter that can be added or not added with a jumper. The Rev C is going to be the epitome of the PEQ1 and the PAFOUR. Also, the PAFOUR will have hi-pass filters and output pots, along with a lower input gain that will work like a pad and go down to -24 dB, which is a pretty good pad. We'll be doing that last mod on the PEQ1s too. Right now you can only go to -18, and with the output pot on the PAFOUR, you'll have a lot more flexibility for gain structuring, both input and output.

Why aren't there more microphone repair techs?

It's a scary thing, and back in my early days of being a studio owner I was frightened about a piece of gear breaking. Fortunately I had a lot of contacts out of the UK who were some of the best recording console and tape machine technicians in the world and I used to have them come over to my house for an extended stay and teach me how to fix equipment. That went on pretty heavily from 1998 to 2000. We were doing stuff like joining two consoles together and recapping tape machines. That was my apprenticeship, although I always repaired things even when I was a kid. I used to send my mics off to get repaired, and believe me, I wasn't always happy with the way they were repaired. I guess by reverse engineering and disassembling things I got to know how they worked. I don't think anybody taught me how to fix mics; I just did it on my own. I guess I'm from the school of mic repairmen who learned by taking everything apart. With any piece of vintage gear I buy, I disassemble it all the way and reassemble it before I even turn it on. I don't know if that's a problem I have or not, but even if it's a Mellotron or Hammond organ, I never plug it in before I take it apart.

What does the future of Wunder Audio look like?

I have about a half dozen full time people working for Wunder, and I have independent contractors who might spend half a year's time working for us, whether it's a machinist, a mechanical engineer or electronic engineer. Those are basically the three kinds of workers we need help from. The whole concept of Wunder Audio is to be a boutique company, so growing into a large company goes against the grain. Some of the products are limited, such as the CM7. There are a finite number of EF14 tubes, and there are a finite number of capsules that M7 expert Siegfried Thiersch — who is now in his 70s — can make. We've got the [mixing] boards coming out, the Wunderbar, but we're only going to make 20 per year for four or five years at the most. Everything that's coming out in the future has been planned and prototyped, but they aren't out yet. One of them is a recreation of the Western Electric mic pre. I have a 12-channel Western Electric board, which is the best tube mic pre I've ever heard. The replica will come out as a module for a board and as a two-channel mic rack piece. Another component is the Wunder Audio compressor, a solid state compressor based on the PEQ1 topology. It'll be like a Neve 2254, but with the Wunder transformers and amplifier stages. It'll have faster attack and release times. Also, we're coming out with a small diaphragm tube microphone, kind of like a KM54. That's going to be a really nice little mic and should be out in 2008. We also have the M49 replica called the CM49 available in limited runs. It's being produced very slowly. Finally, there will be a one-channel version of the PAFOUR, and we're also going to have a four band EQ coming out. If we were a large company with a lot of capital, I guess our products would be ready in a month, but it'll be another two years before everything is out. Everything will have its turn.